1. Field of the Invention
This invention concerns a hot airstream generating device and, more specifically, it relates to a hot airstream generating device using an exhaust gas at high temperature obtained by flameless and complete combustion of a liquefied gas.
2. Description of the Prior Art
Heated air streams have generally been used to conduct shrinking or bonding fabrication for heat-shrinkable plastic tubes, molding of plastic materials, melting of soldering flux, etc. As the apparatus for producing air streams at high temperature (hereinafter simply referred to as a hot blow), those of a structure similar to a so-called hair drier comprising a rotary fan for supplying an air stream and an electrical heater for heating the thus supplied air stream to prepare a hot blow have often been employed.
In the prior hot blow generating device, the air stream supplied from the blower is heated by an electrical heater to a temperature, for instance, from 200.degree. to 300.degree. C. which is suitable to the heat processing of heat-shrinkable tubes, etc. mainly made of polyivnyl chloride resins.
However, as the materials for the heat-shrinkable tubes have gradually been replaced with heat-resistant materials such as silicon rubber type materials, it has become necessary to use a hot blow at a temperature as high as from 400.degree. to 500.degree. C. for heat shrinking these materials. Accordingly, the temperature obtained by the hot blow from the conventional electrically heated type hot blow generating device has become insufficient.
Particularly, in such an application use as covering the bundles of power cables or telephone cables with heat-shrinkable tubes, a considerably greater amount of flow rate at higher temperature is necessary for the hot blow. In this case, the rated electrical power required for the hot blow generating device after amounts to about 800 to 1500 KW assuming that the power source therefor is taken from a commercial AC 100 V line, which increases the energy cost, weight and size, as well as complicates the structure of the device.
Further, the electrically heated device inevitably requires power source cords or like other optional equipment, which further add the weight to the device and enforces labourious and troublesome operations to workers upon handling the device. Furthermore, the commercial power source is not always available in the actual working fields such as buildings under construction, common-use tunnels, etc.
In view of the problems in the electric type hot blow generating device, heat of flames obtained from a gasoline torch or liquefied gas torch has occasionally been used for the fabrication of heat-shrinkable tube or the like, but the use of such flames may possibly lead to fire accidents or undesirably damage the materials to be fabricated.
Therefore, the development for a hot blow generating device, which is based on a new concept, reduced in the size and the weight, convenient to handle with, capable of providing a hot blow at a great flow rate and free from fire danger has long been desired but no suitable device has yet been known or put to practical use up to the present as far as we know.
In the field of the soldering iron, a gas heating apparatus using a liquefied gas as a heat source is disclosed by A. Fujiwara in U.S. Pat. No. 4,133,301 and a further improved heat processing device is also proposed by the present inventor in U.S. Pat. No. 4,552,124. As disclosed in these prior U.S. patents, since the liquefied gas is used as the heat source, a great amount of heat can be attained with a structure relatively small in the size and reduced in the weight. Particularly, since the liquefied gas evaporated from the gas reservoir is burnt completely in a flameless manner by the aid of the combustion catalyst, there is no fire accidents at all.
It may thus be considered, theoretically, possible to apply the prior technics disclosed in the filed of the soldering iron to the hot blow generating device for example, by combining the catalytic combustion device with an appropriate blower.
However, different from the soldering iron, the hot blow generating device has to produce a relatively large flow rate of a hot blow at high temperature and this presents various problems to be solved.
At first, if an air stream of a relatively large flow rate supplied from an air blower is merely and directly applied to the gas combustion device, it will excessively dilute the gas mixture, that is, increase the air/fuel gas ratio in the gas mixture failing to ignite a pilot flame prior to the catalytic combustion reaction.
In addition, a great flow rate of the air stream usually at an ambient temperature will over-cool the combustion catalyst to a temperature lower than the optimum catalytic oxidation temperature thus failing to continue stable catalytic gas combustion.
Further, a great amount of heat is often required, for example, in fabricating heat-shrinkable tubes for covering the bundles of power cables or telephone cables as described above. However, a great amount of liquefied gas required for such use can not spontaneously be evaporized from the gas reservoir only due to the pressure difference between the inside and the outside of the reservoir.
Thus, there are various actual difficulties in applying the technical concept in the aforementioned gas soldering iron to the hot blow generating device as the subject of this invention.